At the molecular level, all known life is made of molecules that follow a consistent structural orientation. Like hands, molecules can be structured in a right or left way. In natural living organisms, DNA is exclusively “right-handed,” while the amino acids forming proteins are “left-handed.” Some researchers are now exploring the concept of constructing life using the opposite handedness to that seen in nature – a phenomenon referred to as “mirror life.”

Building entire mirror organisms is not imminent, but a report published in Science Dec. 12, authored by 38 researchers, including four from Stanford, argues against pursuing this path altogether. This interdisciplinary group – including leading experts in immunology, ecology, evolutionary biology, planetary sciences, biosecurity, policymaking, and synthetic biology – warns of serious risks, such as untreatable infections and irreversible ecosystem disruption.

“The whole possibility of mirror life is far in the future. But by thinking about it now, we can prevent that future completely. Let’s not go there. It’s not worth the risk,” said Mark M. Davis, a co-author of the report and professor of microbiology and immunology in the School of Medicine.

Below, Davis and fellow Stanford co-author Drew Endy, an associate professor of bioengineering in the schools of Engineering and Medicine, discuss the central concerns about mirror life, why their group sounded the alarm now, and what this means for emerging biotechnologies broadly.

For more information about this topic, the authors refer people to the Science perspective and the associated 300-page report. Several authors are convening meetings in 2025 to advance the conversation, including discussions as part of a February 2025 summit at Asilomar in Monterey, California, along with events planned at the Institut Pasteur in France, the University of Manchester in the U.K., and the National University of Singapore.

What are some of the major concerns about mirror life?

Davis: There’s an ongoing research effort to make these mirror proteins for their therapeutic potential, and people aspire to make organisms that could work with mirror proteins. But as we’ve really started thinking about it, we’ve realized that this could be devastating. This could be the ultimate pandemic and largely, if not almost entirely, refractory to immune responses. In other words: Could the immune system see this? The answer is probably not.

There are also concerns that mirror organisms could outcompete existing organisms. There’s a whole ecological disaster scenario there. If they can outcompete single-cell life forms – including bacteria, which are largely good – what does that mean for larger life forms like us?

While the chemical synthesis of mirror proteins poses none of these risks and has lots of plausible benefits, people should not pursue the building of a whole mirror organism. That is too fraught with possible problems.

Why are you raising these concerns about mirror life now?

Davis: We don’t have the knowledge to make mirror organisms at this point. We might in 10 or 20 years, and that’s why it’s good to have these conversations, to say, “Really, we should not advance this.”

Endy: Attempting to build a mirror cell would cost about $500 million. Is that far away or not? It depends. But because no one has yet organized such an effort, now is the time to talk about it. Leadership in emerging technologies requires thinking carefully well before possibilities become likelihoods. Ten years in advance is when you need to speak up and act if you want to have a chance of steering the ship before a single group or country takes a unilateral run at it. I expect critique from the unilateralists who might wish to take that run, calling us chicken. But if you believe the potential risks of a mere mirror microbe, from an ecological perspective, are potentially off-the-charts bad, we need to take it seriously now before anyone acts on it.

What more should people understand about this topic?

Davis: Mirror proteins might be useful. In fact, there already are therapies being developed that use mirror proteins because their reversed chirality makes them very resistant to degradation – to extend the life of a protein drug. So, there are some very benign or even useful applications of mirror work.

But a mirror organism is a potential pathogen. There is no guarantee that we’ll have immunity to such things. There’s no guarantee that they won’t eat up everything in the ecosystem. That’s probably pushing it – but why go there? This is a very, very different kind of synthetic biology that could be very dangerous. It should be isolated and not advanced to building organisms.

Endy: Paul DeMarinis, a colleague in Art and Art History here, was auditing Stanford’s Introduction to Bioengineering course one summer. I was teaching one week on bioterror, bio-error (lab leaks), and bio war. Paul said, “You’ve left out one of the ‘er’s’: bio-scare-er.” I didn’t understand. He explained that the stuff I was talking about is scary. Scary like spiders are scary, like falling from heights is scary. There is an instinctive fear of biotechnology. Paul’s lesson is one of the most profound things I’ve learned.

I am concerned that this report we’ve published could add to a sense of fear related to biotechnology. Yet, I believe strongly and I’m excited about creating opportunities for expressions of fear to come out into the open, so that we can welcome that and engage with those fears constructively. I see no future for bioengineering that doesn’t include the routine building of entire cells. And, so, we have to talk about the edge cases, like mirror life. If we take a more holistic view, the gift of fear is the chance to become courageous together. That is fear’s gift.